1. Field of the Invention
The present invention relates to a zoom camera and, more particularly, to a zoom lens barrel driving system for a lens shutter type camera which can effectively perform the zooming and focusing operations only with one driving source.
2. Description of the Related Art
Generally, compact zoom cameras have a zoom lens barrel driving system with a zooming function of varying magnification, i.e., of varying the focal length of photographing lens, and a focusing function of controlling the focal point in view of the distance between the lens and the object.
Such a zoom lens barrel driving system is disclosed in U.S. Pat. Nos. 4,936,664, 5,602,608 and 5,687,029, respectively.
U.S. Pat. No. 4,936,664 discloses a zoom lens barrel driving system where the zooming and focusing operations are preformed by a zoom motor for varying magnifications and a focus motor for controlling the focus, respectively. FIG. 17 is a graph illustrating the relation of the focal lengths controlled by one driving source to the focal points controlled by another driving source. In the drawing, the horizontal axis line indicates barrel rotation angles, the vertical axis upper-side line indicates focal lengths, and the vertical axis lower-side line indicates focal points. When one motor is driven to vary the focal length, barrel components rotate so that continuous zooming ratio variation occurs from a wide-angle position (Wide) to a telephoto position (Tele) or from the Tele position to the Wide position. In contrast, when another motor is driven to vary the focal point, a focus lever mounted within a shutter block rotates at a predetermined angle within the focusing area to thereby perform the focus controlling operation. In this structure, the zooming and focusing operations are separately performed.
U.S. Pat. No. 5,602,608 discloses a zoom lens barrel system where the zooming, focusing, film winding, and film rewinding operations are performed with one driving source by using separate selection gear mechanisms.
U.S. Pat. No. 5,687,029 also discloses a zoom lens barrel system where the zooming and focusing operations are performed with one driving source. Particularly, in the system, a plurality of grooves are repeatedly formed within the barrel to realize the zooming and focusing areas. FIG. 18 illustrates the relation of the zooming area to the focusing area. In the drawing, the horizontal axis line indicates barrel rotation angles, the vertical axis upper-side line indicates focal lengths, and the vertical axis lower-line indicates focal points. The focusing lengths can be selected step by step at the setting position and the optical field can be realized in accordance with the selected focal lengths. In the optical field realizing area shown in the drawing with a solid line, a front or rear lens group moves along the grooves formed at the barrel so that the focusing position is determined in the area between the near focal point and the infinite focal point.
The zoom lens barrel system disclosed in U.S. Pat. No. 4,936,684 has good efficiency in control because it uses a DC motor having high driving power as the driving source for the zooming operation, and a stepping motor capable of easily providing position-control as the driving source for the focusing operation, but causes an increase in the production cost. The zoom lens barrel system disclosed in U.S. Pat. No. 5,602,608 has a disadvantage in that the complicated structure of the separate selection gear mechanisms is inappropriate for the compact camera use. Furthermore, the zoom lens barrel system disclosed in U.S. Pat. No. 5,687,029 has a disadvantage in that the grooves formed in the barrel affect the operation of the barrel so that inappropriate areas for the photographing optical field are present, making it difficult to perform a continuous zooming operation or to realize a multi-stepped magnification area.